1. Field of the Invention
The invention relates to the field of the inspection and checking of semiconductor wafers or substrates during or after manufacture, or when manufacturing integrated circuits.
2. Description of the Relevant Art
The tendency to increase the diameters of semiconductor wafers means that they have to be handled with extreme care and are increasingly fragile. In addition to this, the increasingly finer etching of patterns on semiconductor wafers makes each component of the wafer increasingly sensitive to manufacturing defects. Conventionally semiconductor wafers are inspected visually by an operator. The human eye is in fact capable of discerning relatively small defects on semiconductor wafers, which to an inexperienced observer have the appearance of a mirror. The higher the quality of manufacture, the more the human eye is capable of identifying small defects. The development of etching techniques towards ever-increasing fineness means that the human eye is reaching its limits, in particular for certain types of defects.
The task of visually inspecting semiconductor wafers is slow, tedious and onerous. In a clean room in which semiconductor wafers are manufactured it is desirable that human presence, a major source of contamination, should be reduced. Inspection machines are generally slow, have relatively poor performance and depend on an operator (and the results are therefore poorly reproducible). Finally, visual inspection does not give rise to sufficient statistical data on the positions, in particular in the plane of the wafer, sizes or types of defects, which is desirable for the statistical monitoring of processes and for searching for the causes of defects or problems.